The project concerns two main lines of investigations: (1) mapping of active sites, binding sites, and receptors on the blood front and tissue front of endothelial cells in selected microvascular beds. The investigation will include (a) anionic sites detectable by cationic tracers and removable by treatment with specific enzymes; (b) active residues of oligosaccharide chains detectable by labelled lactins and removable by treatment with specific enzymes; (c) receptors or binding sites for lipoproteins (LDL, VLDL); (d) receptors or binding sites for vasoactive hormones and amines. (2) Cell fractionation of endothelial cells isolated in mass from the microvasculature of the myocardium (rabbit, calf) and/or skeletal muscle (rabbit). The cell fractions of primary interest are: a plasmalemmal fraction, and a plasmalemmal vesicle fraction. The isolation of plasmalemmal fragments will rely on cationic density modifiers, and/or binding to specific lectins. The fractions will be comparatively analyzed for their lipidic and protein composition, including the proteins involved in the interactions mentioned in the previous section. The final goal is to identify and characterize biochemically and functionally differentiated microdomains in the cellular membrane systems of the vascular endothelium. The information obtained is expected to further our understanding of vascular permeability, interactions of endothelium with platelets and leukocytes, and especially the role of the endothelium in the initiation and development of vascular thrombosis and atherosclerosis.